Digital input represents a code as a digital input code. A digital-to-analog converter (DAC) converts digital input into analog output. The analog output is output as an analog output signal. For analog output, a repeating or periodic waveform may present a problem due to periodicity, i.e., due to being periodic. When the analog output is generated based on digital input in a DAC, mismatch errors among the DAC elements also become periodic. In the frequency domain, the periodic errors may manifest as a smaller number of discrete spectral components or harmonics with higher power, compared to a non-periodic signal, which in turn tends to result in a reduced spurious-free dynamic range (SFDR).
Dither can be added to the digital input to generate a small amount of random noise. For example, dither similar in size or larger than the errors can be added to the digital input before the digital input enters the DAC. This has the effect of “randomizing” the element errors and making them non-periodic, resulting in a larger number of harmonics with lower amplitude levels, spread out over a wider spectrum. This technique can potentially raise the noise floor, but results in a better spurious-free dynamic range.
Dither can be added to the digital DAC input, and then removed by an analog filter at the DAC output.